Dzhokhar Tsarnaev has been found guilty of the Boston Marathon bombing and a US district court jury is to consider a possible death sentence.
A federal jury found Tsarnaev guilty on Wednesday over the terror attack that killed three people and wounded more than 260. He kept his hands folded in front of him and looked down at the defence table in the Boston courtroom as the guilty verdicts were read.
The jury will now decide whether the 21-year-old former student should be sentenced to death or receive life in prison.
Tsarnaev's conviction was widely expected, given his lawyer's startling admission during opening statements that he took part in the bombing. But the lawyer also argued that Tsarnaev's older brother, Tamerlan, masterminded the attack and enlisted his then-19-year-old brother to help.
Prosecutors portrayed the brothers as full partners in a plan to retaliate against the US for its wars in Muslim countries.
Deliberations in the guilt phase began almost two years after twin bombs exploded near the marathon's finish line on April 15, 2013, killing three people and wounding more than 260.
During closing arguments yesterday, Tsarnaev's lawyers agreed with prosecutors that Tsarnaev conspired with his brother to bomb the marathon and planted one of two pressure-cooker bombs that exploded that day.
But the defence said it was his now-dead older brother, Tamerlan, who was the mastermind of the attack. It was Tamerlan who bought the bomb parts, built the bombs and planned the attack, said defence lawyer Judy Clarke.
"If not for Tamerlan, it would not have happened," Ms Clarke said.
A prosecutor told the jury that Tsarnaev made a coldblooded decision aimed at punishing America for its wars in Muslim countries.
"This was a cold, calculated terrorist act. This was intentional. It was bloodthirsty. It was to make a point," Aloke Chakravarty said. "It was to tell America that 'We will not be terrorised by you anymore. We will terrorise you.'"
Ms Clarke argued that Tsarnaev fell under the influence of Tamerlan. She repeatedly referred to Dzhokhar Tsarnaev, then 19, as a "kid" and a "teenager".
Tsarnaev is an ethnic Chechen who moved to the US with his family about a decade before the bombings.
Prosecutors used their closing to remind the jury of the horror of that day, showing photographs and video of the carnage and chaos after the shrapnel-packed pressure-cooker bombs exploded.
In one video, jurors could hear the agonising screams of Krystle Campbell, a 29-year-old restaurant manager who bled to death on the pavement. Another woman and an eight-year-old boy also were killed.
Taking aim at the argument that Tsarnaev was led astray by his older brother, Mr Chakravarty repeatedly referred to the Tsarnaevs as "a team" and "partners" in the attack.
"That day, they felt they were soldiers. They were the mujahedeen, and they were bringing their battle to Boston," the prosecutor said.
Tamerlan Tsarnaev, 26, died four days after the bombings after he was shot by police and run over by Dzhokhar during a getaway attempt. Dzhokhar was captured hours later hiding in a dry-docked boat.